/Engine/Plugins/Runtime/GeometryProcessing/Source/DynamicMesh/Public/Selections/GeometrySelection.h
FGeometrySelectionrepresents a subset of geometric elements of a larger object, for example a Mesh (currently the only use case). The main selection is represented via 64-bit unsigned integers. The integers are stored in aTSetfor efficient unique adds and removals. No assumptions are made about the values, they could be (eg) mesh indices, IDs of some type, or even pointer values.
struct FGeometrySelection
EGeometryElemen...
ElementType
Type of geometric element represented by this selection, if applicable
TSet< uint64 >
Selection
Set of selected items/elements
EGeometryTopolo...
TopologyType
Type of geometric topology this selection is defined relative to, if applicable